The unity of cosmic life and the inevitability of evolved life-forms

The concept of life being a cosmic phenomenon is rapidly gaining support, with new evidence from space science, geology and biology. On this picture life on Earth resulted from the introduction of bacteria from comets and the subsequent evolution of life required the continuing input of genes from comets. By analogy, the case for similar evolutionary developments elsewhere in the universe is explored. The prospects for SETI and Optical SETI are examined in relation to the theory of panspermia.